The present invention relates to a servo system with a positive feedback loop.
There has been devised and demonstrated a servo system which, in addition to a negative feedback loop for applying to a controlled system an actuating signal which is the difference between a controlled variable, which is an output from the controlled system, and a secondary command variable, so as to approach the controlled variable to the secondary command variable, includes a positive feedback loop for generating the secondary command variable by adding to the command the difference obtained by subtracting the controlled variable from the secondary command variable. When this servo system is applied to a one-lag controlled system, the steady state error may be reduced to zero, but in response to a step change in the command, the response of the controlled variable becomes oscillatory. When a one-lag system with a large time constant is inserted into the positive feedback loop in order to avoid this oscillation, the settling time becomes longer.
As described above, the prior art servo system has the defects that the transient error is large and that the settling time is longer even though the steady state error may be reduced zero. Furthermore, when disturbance is applied to the controlled system, the transient error is large and the settling time is longer even though the steady state error becomes zero.